Various methods have been employed in the prior art in attempts to promote the dispersion of ungelatinized starch directly into hot aqueous liquid. Thus, U.S. Pat. No. 3,433,650 to Block and Touher discloses a dry soup mix utilizing a raw starch such as potato starch as the thickening agent, but the starch receives no heat-moisture treatment. Rather, the reference teaches the coating of individual raw starch particles with fat, such as oleomargarine, vegetable oil, or the like, in order to prevent immediate hydration, and thickening of the starch. Dehydrated ingredients in the soups, such as freeze dried chicken, puffed carrots, etc., are shown in the examples, however, all of these appear to require less than 60 seconds for reconstitution.
U.S. Pat. No. 3,116,151 to Giddey discloses a dispersible powdered ready-for-use food composition. Untreated starch is mixed into a melted fat component, dried and pressed into a cake, which is then grated and mixed with particles of soluble constituents. There is no heat-moisture treatment of the starch.
U.S. Pat. No. 2,357,585 to Galvin and Sternfield discloses a food package. The package is an envelope in which the sticky ingredients of the food composition contained therein, i.e., the fats or oil components, form a plastic mass. This plastic mass is positioned at the center of the dry granular components, which may be noodles or the like, to prevent any of the sticky ingredients from adhering to the envelope. In this way, all of the proportioned ingredients are able to be dispensed from the envelope. There is no specific mention of a starch, and no teaching of heat-moisture treatment.
U.S. Pat. No. 4,089,988 to Mostyn, Verrall and Shrimpton, discloses a process for making a dried, granulated dessert-type food composition in which native starch particles and sugar particles are mixed and slightly moistened, then granulated. The granules are then dried, ground and screened to a smaller particle size. It is reported that such free flowing granulated particles will disperse instantly in hot liquid. There is no teaching of any heat-moisture treatment to the starch, nor is the reference specific with respect to the starch used.
U.S. Pat. No. 2,909,431 to Keller discloses a dry mix gravy-type food composition. The reference is specifically concerned with the problem of the lumping of starch when added to a hot liquid. The reference reports to overcome this problem by mixing native starch with a separating material, generally shortening, and some type of leavening ingredient. There is no teaching of heat-moisture treatment of the starch.
The term "heat-moisture-treated starch" is well known in the art, and is commonly used to refer to a starch which has been subjected to a heat treatment under controlled moisture conditions, the conditions being such that the starch undergoes neither gelatinization (i.e., exhibits substantially no loss of birefringence) nor dextrinization. Louis Sair, in Methods in Carbohyrate Chemistry, Vol. IV, R. J. Whistler Ed., Academic Press N.Y. (1964) pp. 283-285, describes laboratory-scale methods for heat-moisture-treated starches, and also describes various properties of starches so treated.
Heat moisture treatment of starches has been employed in food compositions in the past, but such employment has been for the purpose of utilizing the preferred texture and organoleptic properties of such starches rather than their retarded thickening. Thus, U.S. Pat. No. 3,578,497 to Hjermstad discloses the treatment of potato starch by either heating at a constant temperature just below the initial swelling temperature for a long period of time, or, alternatively, heating at a temperature just below the initial swelling temperature and gradually increasing the temperature above the initial heating temperature. Such starches have thickening temperatures as high as 180.degree. F. and are reported to have better consistency characteristics in food uses than untreated potato starch. There is no disclosure of any delayed thickening, nor any indication that such property would allow the addition of a dry food product containing the starch directly to boiling water without lumping of the starch.
U.S. Pat. No. 4,013,799 to Smalligan, Kelly and Enad, discloses a similar heat-moisture treatment of tapioca starch for use in a wet, pre-cooked baby food formulation in order to increase the shelf life of the formulation. The only other starches suggested are grain starches; potato starch and other root starches are not mentioned. The product formulation is not dry, and there is nothing to indicate that the heat-moisture treatment is used to delay thickening.
As is known, heat-moisture-treatment affects various properties of all amylose-containing starches, but perhaps the most dramatic alteration takes place when root or tuber starches, particularly potato starch, are subjected to such a treatment. As has been reported in the literature, when measured as a function of time as with a Barbender Viscograph the "viscosity peak", i.e., the point of maximum viscosity increase during gelatinization, is delayed and also lowered. A starch whose viscosity peak has been delayed in this manner will be referred to throughout the instant specification and claims as a starch having "retarded thickening properties".
It should be noted that retarded thickening properties can be imparted to root starches by various means. One method is to heat an aqueous slurry of starch at just below its gelatinization temperature. This method requires very careful temperature control in order to avoid delatinization of the starch, and therefore it is less practical then the preferred method in which granular starch is treated at temperatures above the gelatinization range, under conditions of moisture and temperature which avoid gelatinization and dextrinization. A recently reported method is disclosed in U.S. Pat. No. 3,977,897 to Wurzburg which involves heating an aqueous slurry of starch at from 50.degree. C. to 100.degree. C., gelatinization being avoided by including in the slurry an appropriate amount of a suitable inorganic salt which raises the gelatinization temperature of the starch. Needless to say, starches so prepared must be thoroughly washed to remove the salts prior to using them in food products.
The most practical commercial method for preparing starches having retarded thickening properties for use in the instant invention is simply to heat starch, at its normal moisture content (or with some added moisture, if desired, but not in aqueous slurry) in a closed heating device, to give the desired degree of heat-moisture-treatment. Specific suitable conditions, and "guidelines" for selecting suitable conditions, will be presented hereinafter.
It should be apparent to those skilled in the art that while the food products of the present invention rely on the retarded thickening properties of the starches contained therein, such teaching may also be used in conjunction with the teachings of the prior art. It should be noted in this regard that the degree of retarded thickening necessary for adequate hot water dispersibility of the starch will also vary with the known effects of other ingredients in any particular food composition, such as fats, sugars, and the like.
Retarded-thickening properties can also be imparted to starch by means of chemical modification, but such methods are costly and may also employ chemicals which are undesirable or even prohibited in food. Because the instant invention relates solely to products intended for human consumption, these last-mentioned chemically-modified starches are generally not considered suitable for use in the invention.